This invention relates to heat exchangers for transferring heat energy between hot and cold working fluids. More specifically, this invention relates to a plate-fin type heat exchanger including means for preventing excessive ice formation at the cold fluid inlet.
In the prior art, plate-fin heat exchangers are well known, and typically comprise a plurality of plates arranged in an alternating stack with extended surface heat transfer elements such as fins or the like. The extended surface fins in the stack are commonly turned alternately at right angles with respect to each other to form closely adjacent flow paths for passage of two working fluids at right angles to each other. This construction is commonly known as a cross-flow heat exchanger, and includes appropriate header bars for isolating the two flow paths from each other together with manifolding for supplying the fluids to their respective flow paths.
A major problem in the design of plate-fin heat exchangers occurs when the cold working fluid is supplied to the heat exchanger at a temperature below the freezing point of water, and the cold fluid includes substantial quantities of entrained water. This problem is prevalent in heat exchangers used on aircraft environmental control systems because of the low air temperatures encountered at high altitudes, or when control system air expanded through a turbine for cooling is supplied to a heat exchanger such as a condensing heat exchanger. Importantly, these types of plate-fin heat exchangers are relatively compact in size, and thus experience an undesirable tendency to collect ice at the cold air inlet face of the unit. Ice formation blocks off fluid flow, and thereby substantially and undesirably reduces the efficiency and operability of the unit.
This invention overcomes the problems and disadvantages of the prior art by providing an improved plate-fin heat exchanger including means for maintaining the temperature of the heat exchanger cold air inlet face at a sufficient level to prevent ice formation.